Here is how to do it if you have Broadcom BCM4311 b/g WLAN (rev 01)
sudo apt-get install linux-firmware linux-firmware-nonfree && sudo modprobe b43 && sudo apt-get install firmware-b43-installer && sudo modprobe b43 && sudo rfkill unblock all
Don't forget to reboot after you launch this line in your terminal window.
The WiFi will come on if put the physical switch from left side in the proper position.
